LEC-06 - 06 Behavioral Combinational Design 2/16/2009...

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06 Behavioral Combinational Design 2/16/2009 © Copyright 2003 Kenneth L. Short 1 2/16/2009 © Copyright 2003 Kenneth L. Short 1 Behavioral Combinational Design Ken Short 2/16/2009 © Copyright 2003 Kenneth L. Short 2 Behavioral Style Architecture ± A behavioral style architecture uses algorithms in the form of sequential programs to describe a system. ± A behavioral description does not directly provide details on how a system is to be implemented. It simply tells how the system is to behave functionally. ± A purely behavioral style architecture consists of one or more process statements. ± Each process statement is, in its entirety, a concurrent statement. Since they are concurrent, processes can execute in parallel. ± Processes communicate with each other using signals, similar to the way components in a structural description use signals to communicate with each other.
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06 Behavioral Combinational Design 2/16/2009 © Copyright 2003 Kenneth L. Short 2 2/16/2009 © Copyright 2003 Kenneth L. Short 3 Processes and Variables ± The statements within a process are sequential statements. They are executed in sequence and their order within the process is critical. ± Variables are objects with a single current value. They are used to store data local to a process. ± Variables in VHDL are similar to variables in conventional programming languages. ± A variable’s value can be changed using a variable assignment statement. 2/16/2009 © Copyright 2003 Kenneth L. Short 4 Process Statement Syntax [ process _label : ] process [ ( sensitivity_list ) ] [ is ] { process_declarative_item } -- process declarativ begin { sequential_statement } --process statement part end process [ process _label ] ;
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06 Behavioral Combinational Design 2/16/2009 © Copyright 2003 Kenneth L. Short 3 2/16/2009 © Copyright 2003 Kenneth L. Short 5 Process Statement ± A concurrent statement consisting itself of sequential statements that represent the behavior of some portion of a design. ± Included in these sequential statements can be statements that call subprograms. ± There are two kinds of processes, those with a sensitivity list and those without. ± Processes used to synthesize logic typically have sensitivity lists. ± Processes used in testbenches don’t typically have sensitivity lists. 2/16/2009 © Copyright 2003 Kenneth L. Short 6 Sensitivity List ± A sensitivity list is a list of signals to which a process is sensitive. ± The order of signals in the sensitivity list is not important. ± Whenever a signal in the sensitivity list changes value, the process is executed. ± The change in value of a signal is referred to as an event on that signal. ± A process with a sensitivity list cannot contain any wait statements. ± A process without a sensitivity list must contain at least one wait statement, or its simulation will never end.
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06 Behavioral Combinational Design 2/16/2009 © Copyright 2003 Kenneth L. Short 4 2/16/2009 © Copyright 2003 Kenneth L.
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This note was uploaded on 08/30/2010 for the course ESE 382 taught by Professor Short during the Spring '10 term at SUNY Stony Brook.

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LEC-06 - 06 Behavioral Combinational Design 2/16/2009...

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